1. Technical Field
The present invention relates to a method of fabricating a thermoelectric device for use in a thermoelectric power generator taking advantage of the Seebeck effect, or a cooler taking advantage of the Peltier effect, and more particularly, to a method of fabricating a small sized thermoelectric device incorporating a plurality of thermocouples.
2. Description of the Related Art
In each of the thermocouples making up a thermoelectric device, a voltage is developed by providing a difference in temperature between the opposite ends thereof This is due to the Seebeck effect, and a device designed to extract the voltage as electric energy is a thermoelectric power generator. The thermoelectric power generator wherein heat energy can be converted directly into electric energy has attracted much attention as effective means of utilizing heat energy, as represented by the case of waste heat utilization.
Meanwhile, the flow of a current caused to occur through a thermocouple results in generation of heat at one end thereof, and absorption of heat at the other end thereof. This is due to the Peltier effect, and a cooler can be manufactured by taking advantage of such phenomenon of heat absorption. This type of cooler which does not comprise mechanical components and can be reduced in size has an application as a portable refrigerator, or a localized cooler for lasers, integrated circuits, and the like.
Thus, the thermoelectric power generator or cooler made up of the thermoelectric device is simple in construction, and is in a more favorable condition for miniaturization as compared with other types of power generators or coolers, offering high usefulness. For example, with the thermoelectric device for use in the thermoelectric power generator, there will not arise a problem of leakage or depletion of electrolyte as with the case of a redox cell, and the thermoelectric device has therefore promising prospects for application to portable electronic devices such as an electronic wrist watch.
The general construction of a conventional thermoelectric device, and a conventional method of fabricating the same, have been disclosed in, for example, Japanese Patent Laid-open Publication No. 63-20880 or Japanese Patent Laid-open Publication No. 8-43555. The description disclosed therein are concerned with a thermoelectric device for use in generation of power. However, the basic construction thereof is the same as that of a thermoelectric device for use in cooling. Hence, the thermoelectric device for use only in generation of power is described hereinafter to avoid complexity in explanation.
In the conventional thermoelectric device disclosed in the publications described above, p-type and n-type thermoelectric semiconductors are alternately and regularly arranged so that a multitude of thermocouples are formed on a horizontal plane, and the thermocouples thus formed are electrically connected to each other in series.
The thermoelectric device is formed in a sheet-like shape by disposing the thermocouples on a plane, and the upper surface and under surface of the thermoelectric device become faces on which hot junctions and cold junctions of the thermocouples are located, respectively. Generation of electric power in the thermoelectric device is caused to occur by a difference in temperature between the upper surface and the under surface of the device having a sheet-like shape.
Meanwhile, an output voltage of a thermocouple using a BiTe-based material, said to have the highest figure of merit of thermoelectric power generation at present, is about 400 xcexcV/xc2x0 C. per couple.
When such thermocouples as described above are employed in a portable electronic device for use at around room temperature, for example, in an electronic watch, a satisfactory difference in temperature can not be expected to be developed inside the device. For example, in the case of a wrist watch, the temperature difference in a wrist watch developed between body temperature and the ambient temperature will be 2xc2x0 C. at most.
It follows that not less than about 2000 couples of BiTe-based thermocouples are required to obtain a voltage not lower than 1.5V, necessary for driving an electronic watch.
Furthermore, in the case of an electronic wrist watch, wherein mechanical components and electric circuit components need to be encased therein in spite of a small internal volume thereof in the first place, it is required that a thermoelectric device for power generation, very small in size, be used.
The conventional method of fabricating a thermoelectric device small in size and composed of a multitude of thermocouples has been disclosed in Japanese Patent Laid-open Publication No. 63-20880.
In the method disclosed, a multi-layered body is formed by stacking p-type and n-type thermoelectric semiconductors, in a thin sheet-like shape, on top of each other in layers while interposing a heat insulating material between respective layers, and then by bonding them together. Subsequently, grooves are formed at a given spacing in the multi-layered body, whereupon the grooves are filled up with a heat insulating material, and connecting portions of individual thermoelectric semiconductors are removed, thereby forming n-type and p-type thermocouples, surrounded by the heat insulating material and isolated from each other. By electrically connecting the thermocouples with each other in series, a thermoelectric device is completed.
Then, in the method disclosed in Japanese Patent Laid-open Publication No. 8-43555, p-type and n-type thermoelectric semiconductors, each having a plate-like shape, are first bonded to separate substrates, and thereafter, a grooving process of forming a multitude of grooves at very small spacings in the longitudinal and transverse directions is applied to respective thermoelectric semiconductors.
As a result of the grooving process described above, a multitude of thermoelectric semiconductors, each columnar in shape, and upstanding regularly on top of the respective substrates, resembling a kenzan (a needle-point flower holder for flower arrangement), are formed. The kenzan-like bodies composed of the n-type and p-type thermoelectric semiconductors, respectively, are thus prepared, and joined together such that the respective thermoelectric semiconductors, columnar in shape, are mated with each other. Thereafter, an insulating material is filled between the respective thermoelectric semiconductors.
In the final step of processing, the substrates are removed, and a thermoelectric device is completed by electrically connecting thermocouples with each other in series.
However, with the methods of fabricating the thermoelectric device as described in the foregoing, there will arise a problem that the material used for the thermoelectric semiconductors is prone to breakage during the process of forming the thermoelectric semiconductors into a sheet-like shape, during the grooving process of forming the kenzan-like bodies, and the like, because of the fragile nature of the material itself for the thermoelectric semiconductors.
In particular, for forming as many as not less than 2000 couples of thermocouples in an ultra-small sized thermoelectric device which can be encased in a wrist watch, it is required that the thickness of the respective sheet-like thermoelectric semiconductors or the diameter of the respective columnar thermoelectric semiconductors be set to on the order of 100 xcexcm or less, and consequently, the problem of fragility described above will become quite serious.
Hence, the present invention has been developed in order to solve such problems as encountered with the conventional methods of fabricating the thermoelectric device, and an object of the invention is therefore to provide a method of fabricating with ease and efficiently a thermoelectric device small in size, but incorporating a multitude of thermocouples so as to be able to output a high voltage.
To this end, a method of fabricating a thermoelectric device according to the invention comprises:
a grooved block fabrication process of forming grooved blocks composed of an n-type thermoelectric semiconductor and p-type thermoelectric semiconductor, respectively, each provided with a plurality of grooves formed at a same pitch and parallel with each other, leaving a depthwise portion of respective grooved blocks intact;
a fitting process of fitting the grooved blocks composed of the n-type thermoelectric semiconductor and p-type thermoelectric semiconductor formed, respectively, by said grooved block fabrication process to each other such that surfaces of the respective grooved blocks, with the grooves formed thereon, face each other;
an adhesion process of forming an integrated block by adhering the grooved block composed of the n-type thermoelectric semiconductor and the grooved block composed of p-type thermoelectric semiconductor, fitted to each other by said fitting process, to each other after filling up gaps in fitting parts between the respective grooved blocks with an adhesive insulation member; and
a thermoelectric semiconductor pieces exposure process of exposing n-type and p-type thermoelectric semiconductor pieces by removing all portions of the integrated block formed by said adhesion process, other than the fitting parts where the grooved block composed of the n-type thermoelectric semiconductor and the grooved block composed of p-type thermoelectric semiconductor are fitted to each other.
When fabricating the thermoelectric device by the method comprising the process described above, thermoelectric semiconductor material having a problem of fragility is always handled in the form of a unit (block). Hence, delicate processing can be applied to the thermoelectric semiconductor material without causing breakage thereof, enabling the thermoelectric device made up of a plurality of thermocouples composed of a plurality of thermoelectric semiconductor pieces very small in size to be efficiently fabricated with ease.
Further, it is preferable that the method according to the invention further comprises a second grooving process of forming a plurality of grooves in the integrated block formed by the adhesion process, in the direction crossing the direction of the grooves formed by said grooved block fabrication process, leaving a depthwise portion of the integrated block intact; a solidification process of filling the grooves formed by the second grooving process with adhesive insulation members and solidifying the same; and, a thermoelectric semiconductor pieces exposure process, to be applied thereafter, of exposing n-type and p-type thermoelectric semiconductor pieces by removing all portions of the integrated block wherein the adhesive insulation members filling up the grooves are solidified in the solidification process, other than the fitting parts where the grooved blocks composed of the n-type thermoelectric semiconductor and p-type thermoelectric semiconductor, respectively, are fitted to each other.
This will result in a considerable increase in the number of thermocouples making up a thermoelectric device of a same size, and the output voltage of the thermoelectric device when used for generation of power can be raised.
It is yet further preferable that the method according to the invention further comprises a grooving process of forming two grooved integrated blocks by forming a plurality of grooves at a same pitch and in the direction crossing the direction of the grooves formed by the grooved block fabrication process, leaving a depthwise portion of respective integrated blocks intact, in each of the two integrated blocks fabricated by means of the grooved block fabrication process, fitting process, and adhesion process described in the foregoing; a second fitting process of fitting the two grooved integrated blocks to each other such that surfaces thereof with the grooves formed thereon face each other; a second adhesion process of forming a second integrated block by filling up gaps in fitting parts between the two grooved integrated blocks fitted to each other by the fitting process with adhesive insulation members, and solidifying the same; and a thermoelectric semiconductor pieces exposure process, to be applied thereafter, of exposing n-type and p-type thermoelectric semiconductor pieces by removing all depthwise portions of the second integrated block, other than the fitting parts.
This will result in a further considerable increase in the number of thermocouples making up a thermoelectric device of a same size, and the output voltage of the thermoelectric device when used for generation of power can be additionally increased.
In the methods of fabricating the thermoelectric device described, the process of forming the grooved block of the n-type thermoelectric semiconductor and grooved block of the p-type thermoelectric semiconductor by applying a grooving process to an n-type thermoelectric semiconductor block and p-type thermoelectric semiconductor block, respectively, such that a plurality of grooves are formed at a same pitch and in parallel with each other, leaving a depthwise portion of the respective blocks intact may be adopted for the grooved block fabrication process described above.
Otherwise, a process of forming the grooved block of the n-type thermoelectric semiconductor and grooved block of the p-type thermoelectric semiconductor by molding n-type thermoelectric semiconductor material and p-type thermoelectric semiconductor material by use of a mold for the grooved block, respectively, and sintering the same, may be adopted for the grooved block fabrication process described above.
In the methods of fabricating the thermoelectric device described, the thermoelectric device can be completed by applying a process of forming electrodes for connecting the exposed n-type and p-type thermoelectric semiconductor pieces to each other alternately and in series after the thermoelectric semiconductor pieces exposure process.
The method of fabricating the thermoelectric device may also comprise a grooving process applied to an n-type thermoelectric semiconductor composite block, prepared by bonding an n-type thermoelectric semiconductor block to a base, and a p-type thermoelectric semiconductor composite block, prepared by bonding a p-type thermoelectric semiconductor block to a base, for forming a plurality of grooves in the n-type thermoelectric semiconductor block and the p-type thermoelectric semiconductor block, respectively, at a same pitch, and to a depth close to the interface between the respective thermoelectric semiconductor blocks and the base thereof; forming an n-type thermoelectric semiconductor composite block and p-type thermoelectric semiconductor composite block, with the grooves formed therein, respectively; and, the fitting process, adhesion process, second grooving process, solidification process, and the like, applied to a pair of thermoelectric semiconductor composite blocks, with the grooves formed therein, forming an integrated block. Or by means of these processes, two integrated blocks may be formed, and fitted to each other after the second grooving process is applied thereto, forming a second integrated block. Thereafter, the thermoelectric semiconductor pieces exposure process of exposing the n-type and p-type thermoelectric semiconductor pieces by removing the respective bases may be applied.
By adopting the processes described above, the thermoelectric semiconductor material can be fully utilized without wastage.
It may be preferable to use bases having a surface area larger than an area of the bonded surface of the respective thermoelectric semiconductor blocks and to interpose spacers between portions of the bases of the n-type thermoelectric semiconductor composite block and the p-type thermoelectric semiconductor composite block, respectively, where the respective thermoelectric semiconductor blocks do not exist, and in the fitting process, controlling a spacing between the bases to be substantially equivalent to the thicknesses of the respective thermoelectric semiconductor blocks.